Also known as the "Jug", the Allies' P-47 Thunderbolt was the biggest, heaviest, and most expensive fighter in history to be powered by a single reciprocating engine. By 1944, it was in combat with the USAAF in every operational theater. Armed with eight .50-caliber machine guns, the P-47 could weigh up to eight tons when fully loaded. Nevertheless, it proved effective in air combat and was especially adept at ground attack. Bubble-top P-47s were nicknamed "Superbolts" by combat pilots in the field.